Method of and device for smoke detection and circuits therefor

ABSTRACT

A smoke detection method and device in which a momentary charging pulse, such as of one-tenth second duration, is intermittently imposed on an ionization chamber, such as once every second to once every 3 seconds. A resistor-capacitor timer coupled with a unijunction transistor produces the momentary, intermittent pulses which are transferred to the chamber through a field effect transistor or a reed relay switch. The current through the ionization chamber triggers a transistor when clear air or no smoke is present, but fails to trigger the transistor when smoke or other types of particles are present. A continuously charging capacitor is discharged when the above transistor fires, but is permitted to become fully charged when the above transistor is not fired. This triggers another unijunction transistor which produces a signal for lighting a lamp, etc. An oscillator produces a different frequency than the a.c. supply line and is coupled therewith to superimpose the oscillations on the supply line, the oscillator stopping when the above signal is produced. A receiver may be plugged into the supply line and receive signals of different frequencies from detectors at different locations, in order to trigger an audible alarm and indicate which detector has detected smoke.

United States Patent Hamm et al.

151 3,657,737 [451 Apr. 18, 1972 THEREFOR [57] ABSTRACT A smoke detection method and device in which a momentary charging pulse, such as of one-tenth second duration, is inter- [72] lnventors: Jeffrey E. Hamm, 1062 South Decatur minemly imposed on an ionization chambern such as P Street Denver, Cola 80219; Harley every second to once every 3 seconds. A resistor-capacitor wakins, 14425 Garden Road Golden timer coupled with a unijunction transistor produces the mo- CO|OI 3040 mentary, intermittent pulses which are transferred to the chamber through a field effect transistor or a reed relay [22] Flled: 1969 switch. The current through the ionization chamber triggers a Appl' 388,281 transistor when clear air or no smoke is present, but fails to trigger the transistor when smoke or other types of particles are present. A continuously charging capacitor is discharged r "340/237 S! & when the above transistor fires, but is permitted to become I fully charged when the above transistor is not fired. This trig- [58] new Search "340/237 5; 250/83'6 F gers another unijunction transistor which produces a signal for 250/44 317/141 5 lighting a lamp, etc. An oscillator produces a different frequency than the ac. supply line and is coupled therewith to [56] Remences C'ted superimpose the oscillations on the supply line, the oscillator UNITED STATES PATENTS stopping when the above signal is produced. A receiver may be plugged mm the supply line and receive signals of different 3,247,375 1966 Lovelock ..250/83.6 FT X frequencies from detectors at different locations, in order to 3,160,866 1964 611 r t --3 S UX trigger an audible alarm and indicate which detector has de- SII'OII S tected smoke 3,500,368 3/1970 Abe "340/237 S Primary Examiner-John W. Caldwell Assistant Examiner- Daniel Myer 10 Claims, 2 Drawing Figures Ar!orney--VanValkenburgh & Lowe Patented April 18, 1972 3,657,737

Harley E. Watkins Jeffrey E. Hamm BY ATTORNEYS This invention relates to a method of and a device for smoke detection and circuits therefor, particularly detection and alarm control circuits, for use in fire detection and alarm equipment.

Numerous devices and circuits have been used or proposed for the detection of a condition indicative of a fire and the production of a signal which actuates an alarm device, such as a visible signal or lamp, an audio signal, such as a horn, buuer or other audio device, as well as the transmission by a separate wire, radio waves or the like to a remote station. Some of these devices have utilized one or more photocells in which the presence of smoke obscuring a light beam directed toward a photocell, or reflecting light from a light beam to a photocell, produces a desired signal. An ionization chamber in which a radioactive material, such as radium sulfate, has also been used, operating on the principle that the alpha rays emitted by the radioactive material will produce a charged path for a slight leakage of current between the oppositely charged, opposite sides of the chamber, and a reduction in the current will be produced by smoke particles entering the chamber. The difference in the current leakage, when air and smoke particles enter the chamber, being on the order of amperes, is so small that it has been thought impossible to utilize directly the change in current flow through a single ionization chamber to produce a reliable signal. Thus, two ionization chambers have been utilized in a voltage divider network, with the first ionization chamber being sealed off and the second supplied with an air flow, which may include smoke, the first and second chambers thus providing a fixed impedance and a variable impedance, respectively. The voltage change is measured at the junction between the two ionization chambers, in order to produce a signal indicative of the presence or absence of smoke in the second chamber. However, this signal is relatively weak and therefore must be amplified, in order to produce an effective alarm initiating signal, but the amplification circuits used therewith are susceptible to error, due to temperature change. Also, the ionization chambers are operated continuously and are thus subject to drift, because of such continuous operation, thereby giving rise to the possibility of error in the signal. These error production possibilities could be avoided, and the detection device and circuit also made much simpler, if a single ionization chamber could be utilized and the changes in current flow therethrough utilized to produce a signal resulting in alarm production.

It has also been proposed, as in U.S. Pat. No. 3,462,752, to utilize a single ionization chamber through which air which may contain smoke is passed, but to operate the ionization chamber continuously to charge a capacitor. A condenser and variable resistor in series are utilized in a timing circuit, to intermittently close a relay switch and discharge the capacitor substantially completely, with additional timing circuits necessary to receive the discharge of the capacitor and actuate an alarm device, when the charge on the capacitor is lower than normal. However, such a circuit requires a pair of unijunction transistors which must be normally maintained at a voltage which is exceedingly close to the triggering voltage, with the result that any slight variation in the signal produced by discharging the capacitor may trigger the unijunction in error and thus result in a false alarm or to prevent the unijunction from triggering and thus fail to produce an alarm signal which should be given, Le, a non-alarm condition. Thus, such a circuit is particularly susceptible to the efiect of static charges which tend to prevent such a unijunction from triggering and thereby produce a non-alarm condition. Such a unijunction operating close to its triggering point also has a relatively high impedance and thus may be unduly affected by temperature changes. Charging the capacitor continuously through the ionization chamber again introduces the possibility of error through drift. In addition, the connection of the ionization chamber to the positive lead, required by the capacitor being charged to be connected to the negative lead, requires all contacts and also the chassis to be isolated, thus involving difficulties in installation and also producing difficulties in operating such a detector with other equipment, such as a burglar alarm. Among the objects of this invention are to provide a novel method of and device for smoke detection, utilizing a single ionization chamber; to provide such a method and device in which the possibility of drift in the ionization chamber is substantially eliminated; to provide such a device and circuit therefor in which the adverse effect of static is substantially eliminated; to provide such a device which is compatible with other types of devices which may be operated in conjunction therewith; to provide such a device and circuit therefor which is not adversely afi'ected by temperature changes; to provide such a device and circuit therefor which is usable with a conventional l 10 volt AC source of electricity; to provide such a device and circuit therefor which is particularly usable with means for producing a signal of a frequency which may be superimposed on a 60 cycle AC line to operate a receiver at a remote location; to provide such a device and circuit therefor which may exist in more than one form; and to provide such a method and device, as well as a circuit therefor, which are effective and efficient in operation.

Additional objects of this invention, as well as additional features thereof, will become apparent from the description which follows, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram of a detection device, including an electronic circuit, constructed in accordance with this invention; and

FIG. 2 is a circuit diagram of an 'altemative detection device and circuit, showing also one form of signal producing device which is conveniently used therewith.

In general, the method of this invention includes intermittently charging an ionization chamber through which air which may contain smoke is passed, and utilizing the current flow through the chamber to trigger an electronic switching device, when the current flow is less than a predetermined amount due to the presence of smoke particles in the air passed through the ionization chamber. The intermittent charging of the ionization chamber is by an impulse having a duration of a fraction of a second, as on the order of one-tenth of a second, while the impulses are repeated at predetermined time periods of considerably longer duration, such as every 1 second toevery 3 seconds. The electronic switching device, which is triggered by the current flow through the ionization chamber when clear air is present, is not triggered when the current through the ionization chamber is reduced by the presence of smoke particles or the like.

The above method may be carried out by the smoke detection device illustrated in either FIG. 1 or FIG. 2. Each device includes an ionization chamber I which is intermittently charged for a fraction of a second and the current flow measured to determine whether an alarm is to be triggered. The circuit of FIG. 1 includes a positive lead 10 and a negative lead 11, maintained at a suitable voltage, such as 12 volts, and between which the components are connected. The ionization chamber I includes a wall 12 and an electrode 13which carries a small amount of radioactive material, such as Americium, which may be found to be preferable, because it emits essentially alpha rays, although radium sulfate or other radioactive material may be substituted therefor. The ionization chamber I is connected between the source electrode of a field effect transistor 14 and the negative lead 11, with the drain electrode of PET 14 being connected to the base of a PNP transistor 15 whose emitter electrode is connected to the positive lead 10 and whose collector electrode is connected through a resistor 16 with the negative lead 11, so that normally, when the charge is impressed on the ionization chamber I through the FET 14, the resulting current passing through the ionization chamber will trigger the transistor 15. The timing of the charges intermittently applied to the ionization chamber I is supplied through a timing circuit which includes a condenser 17 connected to the negative lead 11, and

also, through a junction connected to the emitter of a unijunction 18, with a variable resistor 19, which is also utilized as a sensitivity adjustment for the detector, essentially controlling the time periods of the impulses to the ionization chamber I. A resistor 20, in series with resistor 19, prevents the full 12 volts from being applied to the emitter of unijunction transistor 18, while a variable resistor 21, preferably preset at the factory, determines the range of adjustment which may be made by the variable resistor 19. For instance, the resistor 21 may be preset, so that variable resistor 19 may be utilized to vary the time of charges applied to the ionization chamber I between once every second and once every 3 seconds. A resistor 22 connected between the unijunction transistor 18 and the positive lead establishes the triggering point or bias of unijunction 18, while a resistor 23 connected between unijunction 18 and the negative lead 11 is utilized to develop a voltage drop, when unijunction 18 fires. A current limiting resistor 24 is located between unijunction 18 and the gate electrode of the FET 14, while a resistor 25, connected between the gate electrode of the FET l4 and ground lead 11, combines with resistor 24 to provide a voltage divider, to produce the proper voltage for operation of the FET 14. It may also be noted that the off resistance between the drain and the source of the F ET 14 should be at least 10 ohms as a minimum, to eliminate leakage between the ionization chamber I and the transistor 15. As will be evident, depending upon the adjustment of resistor 19, a voltage impulse will be applied between the wall 12 and electrode 13 of the ionization chamber I intermittently, as the unijunction 18 fires and triggers the FET 14, in turn causing the transistor 15 to fire and current to flow through resistor 16 when clear air passes through ionization chamber l. In this connection, it will be noted that should the ionization chamber be charged continuously or even for an unduly long time period, such as l second, the transistor would be unable to determine the difierence between the current produced when clear air and smoky air or smoke is present, since the impedance between the emitter and base of the transistor is so low that a permanent or substantially permanent connection to the chamber would cause the signal to be shunted across the supply voltage.

When transistor 15 fires, a condenser 27 couples the signal developed across resistor 16 to the gate of an SCR 28, with a resistor 29 connected between the gate and ground lead 11, to maintain the gate at a low impedance and thereby prevent false triggering of the SCR by a transient current. The cathode of SCR 28 is connected to ground, while the anode is connected to a junction between a timing capacitor 30 and a resistor 31, with the former being connected to the ground lead 11 and the latter to the positive lead 10. Thus, the SCR 28 is connected in parallel with the timing capacitor 30, so that when a signal is produced at the gate of the SCR under clean air conditions, the SCR 28 keeps capacitor 30 discharged to a low level, such as approximately 1 volt. The resistor 31 should have a value ,so that the SCR 28 will trigger but will not lock up", i.e., lock as a short, and stay in on" condition. Thus, the SCR 28 is utilized as an on-off" switch. On the opposite side of the above junction is a resistor 32, which is a current limiting resistor, to prevent excessive voltage at the gate of an SCR 33, which acts as a triggering switch and to which resistor 32 is connected. A resistor 34 and a condenser 35, each connected between the gate of SCR 33 and ground, respectively cause a low impedance to be developed at the gate of SCR 33 and prevent transients and spikes from being transmitted to the gate. The cathode of the SCR 33 is connected to ground, while the anode is connected to what may be referred to as a triggering junction 36. Also, the positive lead 10 is connected to a positive junction 37, while the negative lead 11 is connected to a negative junction 38.

As indicated previously, when there is clear air or a no smoke condition, the SCR 28 maintains capacitor 30 discharged to a low level, such as 1 volt, so that insufficient current will flow through resistor 32 to trigger the SCR 33, and no signal will be produced at triggering junction 36. In this connection, it will be noted that the capacitor 30 and resistor 31, in conjunction with the SCR 33, form a timing circuit which normally causes the SCR 33 to fire at predetermined time intervals, as when capacitor 30 reaches a 6 volt level. However, the relative values of the capacitor 30 and resistor 31 are selected so that the time period of this timing circuit is in excess of the time period of the timing circuit which includes condenser 17 and resistor 19, such as about 5 or 6 seconds compared with the l to 3 second timing interval of the latter. Thus, when smoke enters the ionization chamber I and the flow of current across the chamber is thereby reduced, there will be insufficient current to trigger transistor 15 and SCR 28 will not fire, so that capacitor 30 will continue to charge, as at 6 volts or approximately when the predetermined period of this timing circuit expires, thereby causing SCR 33 to fire and produce a signal at the triggering junction 36. A further advantage of the 5 to 6 second time delay provided by the timer which includes capacitor 30 is that, if what may be termed a false alarm is produced, e.g., a lack of a signal at SCR 28 on occurrence of one impulse by the timer which includes capacitor 17, this condition will be corrected on the next pulse in charging ionization chamber 1, since the capacitor 30 has not yet had an opportunity to become fully charged and thereby trigger SCR 33, because previous triggering of SCR 28 has reduced capacitor 30 to a low level. Thus, assuming that the timer which includes capacitor 17 is set to produce an impulse every 2 seconds and that the timer which includes capacitor 30 is set to pulse SCR 33 every 5 seconds, it will be necessary for the same condition to be repeated on a second impulse, before SCR 33 will be triggered. Of course, with a shorter period for the intermittent charges supplied to ionization chamber I, there may be three or more successive charges of the ionization chamber before SCR 33 will be triggered. Thus, any momentary errors produced in the circuit will not affect the operation of the device.

In the alternative device and circuit of FIG. 2, the timer for intermittently charging the ionization chamber I is similar, thus including condenser 17, adjustable resistor 19, resistor 20 and preset adjustable resistor 21 connected across the positive lead 10 and negative lead 11, together with the unijunction transistor 18 and resistor 22. However, instead of the FET 14 of FIG. 1, a normally open switch 40, as of the reed type, is connected between the base of transistor 15 and the electrode 13 of the ionization chamber, while a relay coil 41 is energized to close switch 40. A diode 42 is shunted across coil 41, to prevent secondary closure of the contacts through field collapse, it being noted that diode 42 forms a short across the coil 41 in one direction only. As before, the current passing through the ionization chamber I, upon charging thereof, may trigger transistor 15, with this signal being coupled to the gate of SCR 28 by condenser 27, and resistors 16 and 29 being placed in the circuit for the purpose previously described. Also, capacitor 30 and resistor 31 have the same function as before, but the junction between resistor 31 and SCR 28 is connected to the emitter of a unijunction transistor 43, with a condenser 44 connected therebetween and ground, to inhibit transients or static from the emitter. Unijunction transistor 43 is essentially a timing switch, while a resistor 45 establishes the bias or triggering point of the unijunction and a resistor 46 establishes a low impedance at the gate of the SCR 33 and also establishes a signal which will trigger the SCR 33. Resistors 45 and 46 are connected between the opposite bases of unijunction 43 and the ground lead 10 and negative lead 11, respectively, while condenser 35 again prevents transients and spikes from adversely affecting the gate of SCR 33.

As before, when clear or smoke free air passes through the ionization chamber I and the ionization chamber is intermittently and momentarily charged, the signal from transistor 15 to SCR 28 will cause the latter to discharge condenser 30, so that SCR 33 will not fire. However, if smoke is present in the air passing through the ionization chamber, the current produced will be insufficient to trigger transistor 15 and SCR 28 will not fire, so that capacitor 30 will continue to charge,

and if not discharged by a signal indicating clear air, then SCR 33 will fire when capacitor 30 reaches a 6 volt level, thereby producing a signal at triggering junction 36. Such a signal may cause a lamp 47, for instance, to be lighted and may also actuate any other type of device.

The power supply to the positive and negative junctions 37 and 38 of FIG. 1 may be similar to that illustrated in FIG. 2, in which wires 50 and 51 may be connected to a suitable source of alternating current, as at 1 l0 volts, 50 to 60 cycles, with a fuse 52 connected in one wire and a grounded condenser 53 connected with the other wire, the latter coupling the circuit to ground or to the case in which the circuit is installed, to act as a shield against static. Wires 50 and 51 are connected to the primary of a transformer 54 having a secondary adapted to produce 24 volts, and across which a full wave, diode rectifier 55 is installed. A normally closed reset switch 56 is connected to the negative side of the rectifier, with a wire 57 extending therefrom to the negative junction 38, while a 24 volt wire 58 connects the positive side with lamp 47. A voltage dropping resistor 59 is also connected to the positive side of the rectifier, to supply 12 volts to the positive junction 37 of lead through a wire 60, while a voltage regulating, Zener diode 61, to maintain the voltage at not more than 12 volts, is connected between junction 37 and negative lead 11. A condenser 62 is connected between wires 57 and 60 as a filter condenser, to remove AC components, while bypass condenser 63 is similarly connected to eliminate static and transients. Thus, a full wave rectified DC current of not more than 12 volts is impressed between the junctions 37 and 38. The triggering signal at trigger junction 36 may initiate an audible alarm or produce an alarm signal at a remote place, as well as cause lamp 47 to be lit. Thus, an oscillator may be activated, or the oscillator may operate continuously, to send a high frequency signal superimposed on the 60 cycle AC supplied through wires 50 and 51, to be picked up by a receiver which is plugged into the AC supply line. Such a receiver, which is responsive to the oscillator signal, may be located at a remote point, such as in another room or at a different location in a factory or other building. Several such smoke detection units may be utilized, as in different rooms, but each adapted to actuate both an alarm light and an audio signal alarm at a remote station. The receiving unit at the remote station is desirably constructed in accordance with the disclosure of the Harley E. Watkins application for U.S. Pat. Ser. No. 872,059, filed Oct. 29, 1969, and now abandoned, and entitled Electrical Warning Device. As described therein, when three detectors are used, the oscillators thereof may be tuned to resonate at 30, 50 and 70 kilocycles. If a larger number of detectors is used, each may be tuned to any one of a selected array of frequencies such that the output of one detector will not interfere with the output of another detector. Thus, the receiver may be provided with means for responding to the frequency of a particular detector and causing a lamp or other visual indicator to be energized, indicating which of the detectors has produced an alarm signal. Also, the receiver may be constructed so that an audible alarm signal will also be activated. Such a receiver is also preferably constructed so that it will receive a continuous signal from each detector and will actuate the alarm when the signal ceases. Thus, the oscillator of FIG. 2 is constructed to continuously send a signal until terminated by the signal produced at triggering junction 36.

The oscillator of FIG. 2 is coupled to the respective wires 50 and 51 by wires 65 and 66, which lead to the secondary of a transformer 67, with coupling condensers 59 and 60, respectively, installed in the lines. The oscillator includes an NPN transistor 70 and a condenser 71, with condenser 71 being connected across the primary of transformer 67 and the collector electrode of transistor 70 being connected to one side of the transformer primary. A feedback condenser 72 is connected between the base of transistor 70 and the opposite side of the primary coil of transformer 67, this feedback condenser causing the transistor 70 to oscillate, with the frequency of oscillation being determined by the condenser 71 and transformer 67. The base of transistor 70 is connected to the triggering junction 36, through a diode 73, which permits unidirectional current flow only. A wire 74 connects the positive side of the full wave rectifier, through a resistor 75, with the center tap of the primary of transfonner 67, to produce a low impedance and thereby prevent unduly loading the coil. Resistor 75 limits the current which must be handled by the oscillator, while a filter condenser 76 is connected between wire 74 and the negative side of the rectifier. Biasing resistors 77 and 78 are connected between the base of transistor 70 and the transformer center tap wire 74 and the 12 volt negative lead 11, respectively, to provide a voltage divider network, in order to establish the proper operating bias on the transistor 70. The emitter electrode of transistor 70 is connected through a current limiting resistor 79 to negative junction 38, in order to prevent excess current from flowing through the transistor.

As will be evident, when smoke is contained in the air passed through ionization chamber 1 and the SCR 33 is triggered to produce a signal at the triggering junction 36, in the manner previously described, not only will lamp 47 be lit, but also current may leak to the base of transistor 70 through unidirectional diode 73 from the triggering point, and the oscillator signal will be discontinued, due to the base of transistor 70, in effect, being grounded. The parts of the oscillator, particularly transformer 67 and condenser 71, may be chosen so that a signal of a particular frequency will be produced, as indicated previously. The signal thus generated will pass through coupling condensers 68 and 69 and thence through wires 65 and 66 to the AC line wires 50 and 51, for transmission to a receiver.

An advantage of the circuit of FIG. 2, in which a signal is sent continuously but is discontinued when an alarm is to be produced, lies in the fact that upon the cessation of current supply through the wires 50 and 51, the signal will automatically cease, thus being reflected in the receiver. Thus, the continuous operation of the oscillator is indicative that the device is in operation. Also, should any critical component fail, the

oscillation signal will be discontinued, indicative of the fact that repair or correction should be made to the unit involved. Thus, substantially total supervision of the unit is provided.

The types of the various electronic switches may, of course, vary considerably, although in actual circuits constructed in accordance with this invention, the unijunction transistors 18 and 43 were each 2N4852 and the field effect transistor 14 was 2N4093, with transistor 15 being 2N3248, although 2N2894 could be used, and transistor 70 being MPS27l2, although 2N2476 or 2N2477 could be used. Both SCR 28 and SCR 33 were 2N5060, with diode 73 being SCE-l and Zener diode 61 being M3l000-15. Resistors 22 and 45 were specially selected so that unijunction transistors 18 and 43, respectively, each would break at 50 percent of the supply voltage. ()ther resistors had the following values:

The following capacitors had the following values:

Capacitor: 17 27 l5 mfd. 0.02 mfd.

30 I mfd. 35 0.02 mfd. 44 0.02 mfd. 62 I00 mfd. 63 0.02 mfd. 76 33 mfd.

In connection with the above, it will be noted that'condenser 62 was a tantalum filter condenser, while condenser 63 was a ceramic condenser.

For a 50 kilocycle oscillator, the following capacitors had the following values:

Capacitor:

68 0.005 mfd. 69 0.005 mfd. 71 430 t. 72 330 pf.

From the foregoing, it will be evident that the method of and device for smoke detection and circuits therefor of this invention fulfill the objects and requirements hereinbefore set forth to a marked degree. Through the intermittent and momentary charging of the ionization chamber, which may also be referred to as an ionization area, the transistor or other electronic switch is capable of distinguishing between current flow through the ionization chamber when clean air is present and when particles of smoke or the like are present, the air being supplied by natural convection or in any other suitable manner. The timer which controls the interval between the charging pulses may be adjusted, as through variable resistor 19, to cause the detector to respond to different amounts of smoke or other particles in the air. Thus, it has been found that when the charging pulses occur one each second, a much smaller number of smoke particles will cause a smoke indication signal to be produced than when the charging pulses are impressed across the ionization chamber at greater time intervals. This is of advantage in situations where a small amount of particles, for instance, are normally in the air and the detector is to be set for an indication of a greater number of particles. Through the connection of the ionization chamber to the negative lead, difficulties in mounting the unit and in associating the unit with other types of devices are avoided. Also, due to the fact that neither the unijunction transistor 18, FET l4, transistor 15, SCR 28, unijunction transistor 43 nor SCR 33 is required to be maintained at a voltage which is close to the triggering voltage, slight variations in the signals thereto do not adversely affect the operation thereof. Through the operation of the timer which includes the capacitor 30 at a greater time period than the timer which controls the charting impulses to the ionization chamber, a check on the reaction of the transistor 15 to the current of the ionization chamber is provided, since normally at least two indications of smoke must be produced, in order to trigger an alarm signal. The intermittent charging of the ionization chamber further reduces error due to drift, while the effect of static or transients is greatly minimized. The circuit is not subject to undue variations because of temperature changes. The detector is particularly adapted to be supplied with rectified current from a conventional AC source and thus may be associated with an oscillator adapted to produce a signal of a different frequency, which is superimposed on the AC supply line, although to provide more complete supervision, the oscillator is preferably adapted to operate until a smoke indicating signal is obtained, then discontinue oscillation. The method of this invention is also adapted to be carried out by more than one device, although the detection device of FIG. 1 has an advantage over the detection device of FIG. 2 in that no moving parts are required, and it is thus easier to construct and maintain. The FET 14 of FIG. I and associated resistors may, of course, be substituted for the reed switch 40 and relay coil 41 of FIG. 2, while the unijunction transistor 43 and associated resistors and condenser may be utilized in the circuit of FIG. 1.

As will be evident, the detector of this invention may be utilized to detect particles other than smoke, carried by air or any other gas or vapor, thereby being adaptable to industrial or other types of operations in which the detection of the presence of particles of types other than smoke particles is desirable. It will also be evident that, although two different embodiments of the detection device have been illustrated and described, other embodiments may exist and various changes made therein, without departing from the spirit and scope of this invention.

What is claimed is: 1. A method of detecting smoke and the like in air or the like, which comprises:

establishing an ionization area; supplying air or the like, which may contain particles of smoke or the like, to said area, so that said air or the like will tend to become ionized; intemtittently impressing a voltage momentarily across opposite sides of said area so that a current will flow between said opposite sides due to ionization of said air, with the presence of particles of smoke or the like in said air or the like reducing the current flow; and passing such current to an electronic switch to trigger the same when such current is equal to or greater than a predetermined amount, but will not trigger the same when less than said predetermined amount, due to the presence of smoke or the like in said ionization area. 2. A method as defined in claim 1, wherein: said voltage is impressed across said ionization area for a period on the order of one-tenth second and at intervals on the order of once every second to once every 3 seconds. 3. A device for detecting smoke and the like, comprising: an ionization chamber having means for ionizing air or the like supplied thereto; means for impressing a voltage intermittently and momentarily across said ionization chamber so that a current will flow through said ionization chamber, said current flow being in a reduced amount when smoke particles or the like are present in said air or the like; an electronic switch connected to said chamber so as to be responsive to said current flow and to trigger when said current reaches a value corresponding to substantially clean air or the like; and means responsive to a predetermined condition of said electronic switch for producing a signal indicative of the presence of smoke or the like in said ionization chamber. 4. A device as defined in claim 3, wherein: said means for impressing voltage across said ionization chamber includes a timer and a switching means connected to said chamber. 5. A device as defined in claim 4, wherein: said timer includes capacitor means, resistor means and electronic switching means. 6. A device as defined in claim 5, wherein: said switching means connected to said chamber includes a physically movable switch and a relay coil for moving said switch. 7. In a device as defined in claim 5, wherein: said switching means connected to said chamber includes a field effect transistor having a source electrode connected to said chamber and a gate connected to said electronic switching means of said timer. 8. In a device as defined in claim 3, wherein said means includes:

an electronic switch adapted to produce said signal; a capacitor and a resistor associated therewith to provide a timer associated with said electronic switch; means for charging said capacitor continuously; and means for discharging said capacitor when said electronic switch connected to said chamber is triggered, whereby said electronic switch for producing said signal will be activated in the absence of triggering of said electronic switch connected to said chamber. 9. A signal and detection circuit for smoke and the like, including:

a device for detecting smoke and the like including:

responsive an ionization chamber having means for ionizing air or the like supplied thereto;

means for impressing a voltage intermittently and momentarily across said ionization chamber so that a current will flow through said ionization chamber, said current flow being in a reduced amount when smoke particles or the like are present in said air or the like;

an electronic switch connected to said chamber so as to be responsive to said current flow and to trigger when said current reaches a value corresponding to substantially clean air orthe like;

means responsive to a predetermined condition of said electronic switch for producing a signal indicative of the presence of smoke or the like in said ionization chamber;

said circuit further including:

an AC supply and rectifying means for supplying electricity to a positive lead and a negative lead for a circuit including said detection device;

an oscillator for producing electrical oscillations having a frequency different from and distinguishable from the frequency of said AC supply;

means coupling the output of said oscillator with said AC supply line; and

means connecting said oscillator with said responsive means, for discontinuing the operation of said oscillator upon the production of a signal indicative of the presence of smoke or the like in said ionization chamber.

10. A signal and detector circuit for indicating smoke and the like in air and the like, including:

a device for detecting smoke and the like, including: an ionization chamber having means for ionizing air or the like supplied thereto;

means for impressing a voltage intermittently and momen- V tarily across said ionization chamber so that a current will flow through said ionization chamber, said current flow a second electronic switch responsive to a predetermined condition of said first electronic switch for producing a signal indicative of the presence of smoke or the like in said ionization chamber;

a capacitor and a resistor associated with said second electronic switch to provide a timer;

means for charging said capacitor continuously;

means for discharging said capacitor when said first electronic switch connected to said chamber is triggered, whereby said second electronic switch for producing said signal will be activated in the absence of triggering of said first electronic switch connected to said chamber;

said circuit further including:

an AC supply and rectifying means for supplying electricity to a positive lead and a negative lead for a circuit including said detection device;

an oscillator for producing electrical oscillations having a frequency different from and distinguishable from the frequency of said AC supply;

means coupling the output of said oscillator with said AC supply line; Y

means connecting said oscillator with said responsive means for discontinuing the operation of said oscillator upon the production of a signal indicative of the presence of smoke or the like in said ionization chamber; and

a lamp connected to said rectifier means arranged to be supplied with current in response to said signal. 

1. A method of detecting smoke and the like in air or the like, which comprises: establishing an ionization area; supplying air or the like, which may contain particles of smoke or the like, to said area, so that said air or the like will tend to become ionized; intermittently impressing a voltage momentarily across opposite sides of said area so that a current will flow between said opposite sides due to ionization of said air, with the presence of particles of smoke or the like in said air or the like reducing the current flow; and passing such current to an electronic switch to trigger the same when such current is equal to or greater than a predetermined amount, but will not trigger the same when less than said predetermined amount, due to the presence of smoke or the like in said ionization area.
 2. A method as defined in claim 1, wherein: said voltage is impressed across said ionization area for a period on the order of one-tenth second and at intervals on the order of once every second to once every 3 seconds.
 3. A device for detecting smoke and the like, comprising: an ionization chamber having means for ionizing air or the like supplied thereto; means for impressing a voltage intermittently and momentarily across said ionization chamber so that a current will flow through said ionization chamber, said current flow being in a reduced amount when smoke particles or the like are present in said air or the like; an electronic switch connected to said chamber so as to be responsive to said current flow and to trigger when said current reaches a value corresponding to substantially clean air or the like; and means responsive to a predetermined condition of said electronic switch for producing a signal indicative of the presence of smoke or the like in said ionization chamber.
 4. A device as defined in claim 3, wherein: said means for impressing voltage across said ionization chamber includes a timer and a switching means connected to said chamber.
 5. A device as defined in claim 4, wherein: said timer includes capacitor means, resistor means and electronic switching means.
 6. A device as defined in claim 5, wherein: said switching means connected to said chamber includes a physically movable switch and a relay coil for moving said switch.
 7. In a device as defined in claim 5, wherein: said switching means connected to said chamber includes a field effect transistor having a source electrode connected to said chamber and a gate connected to said electronic switching means of said timer.
 8. In a device as defined in claim 3, wherein said responsive means includes: an electronic switch adapted to produce said signal; a capacitor and a resistor associated therewith to provide a timer associated with said electronic switch; means for charging said capacitor continuously; and means for discharging said capacitor when said electronic switch connected to said chamber is triggered, whereby said electronic switch for producing said signal will be activated in the absence of triggering of said electronic switch connected to said chamber.
 9. A signal and detection circuit for smoke and the like, including: a device for detecting smoke and the like including: an ionization chamber having means for ionizing air or the like supplied thereto; means for impressing a voltage intermittently and momentarily across said ionizaTion chamber so that a current will flow through said ionization chamber, said current flow being in a reduced amount when smoke particles or the like are present in said air or the like; an electronic switch connected to said chamber so as to be responsive to said current flow and to trigger when said current reaches a value corresponding to substantially clean air or the like; means responsive to a predetermined condition of said electronic switch for producing a signal indicative of the presence of smoke or the like in said ionization chamber; said circuit further including: an AC supply and rectifying means for supplying electricity to a positive lead and a negative lead for a circuit including said detection device; an oscillator for producing electrical oscillations having a frequency different from and distinguishable from the frequency of said AC supply; means coupling the output of said oscillator with said AC supply line; and means connecting said oscillator with said responsive means, for discontinuing the operation of said oscillator upon the production of a signal indicative of the presence of smoke or the like in said ionization chamber.
 10. A signal and detector circuit for indicating smoke and the like in air and the like, including: a device for detecting smoke and the like, including: an ionization chamber having means for ionizing air or the like supplied thereto; means for impressing a voltage intermittently and momentarily across said ionization chamber so that a current will flow through said ionization chamber, said current flow being in a reduced amount when smoke particles or the like are present in said air or the like; a first electronic switch connected to said chamber so as to be responsive to said current flow and to trigger when said current reaches a value corresponding to substantially clean air or the like; a second electronic switch responsive to a predetermined condition of said first electronic switch for producing a signal indicative of the presence of smoke or the like in said ionization chamber; a capacitor and a resistor associated with said second electronic switch to provide a timer; means for charging said capacitor continuously; means for discharging said capacitor when said first electronic switch connected to said chamber is triggered, whereby said second electronic switch for producing said signal will be activated in the absence of triggering of said first electronic switch connected to said chamber; said circuit further including: an AC supply and rectifying means for supplying electricity to a positive lead and a negative lead for a circuit including said detection device; an oscillator for producing electrical oscillations having a frequency different from and distinguishable from the frequency of said AC supply; means coupling the output of said oscillator with said AC supply line; means connecting said oscillator with said responsive means for discontinuing the operation of said oscillator upon the production of a signal indicative of the presence of smoke or the like in said ionization chamber; and a lamp connected to said rectifier means arranged to be supplied with current in response to said signal. 